NDA (I) 2025 General Ability Test · Question 146 of 150

Correct — D, this is the incorrect statement. An ideal ammeter has very LOW resistance and a voltmeter very HIGH resistance — statement (d) reverses this and is therefore wrong. An ammeter is put in series and must have low resistance so it does not reduce the current it measures; a voltmeter is put in parallel and must have high resistance so it draws almost no current from the branch it measures.

• (a)An ammeter is always connected in series in the circuit to measure the current — This is correct — an ammeter is connected in series so the whole current passes through it, so it is not the wrong statement.
• (b)A voltmeter is always connected to parallel in a circuit to measure the voltage — This is correct — a voltmeter is connected in parallel (across the component) to read the potential difference, so it is not the wrong statement.
• (c)A voltmeter has a high resistance and an ammeter has a low resistance — This is the correct pairing (voltmeter high, ammeter low), so it is not the statement being sought.

An ammeter measures current and is placed in series, so it must have very low (ideally zero) resistance to avoid altering the current. A voltmeter measures potential difference and is placed in parallel across a component, so it must have very high (ideally infinite) resistance to avoid drawing current and disturbing the reading. A galvanometer is converted into an ammeter by a low-resistance shunt in parallel, and into a voltmeter by a high resistance in series.

Three statements are true and one flips the resistance rule. The pairing to hold onto is that a series meter with low resistance is the ammeter, while a parallel meter with high resistance is the voltmeter. Statement (d) swaps the resistances, making it the incorrect one.

• An ammeter is connected in series and has low resistance (ideal value zero).
• A voltmeter is connected in parallel and has high resistance (ideal value infinite).
• A galvanometer becomes an ammeter with a low-resistance shunt in parallel.
• A galvanometer becomes a voltmeter with a high resistance in series.

• Swapping the resistances — ammeter is low, voltmeter is high, not the reverse.
• Mixing up the connections — ammeter in series, voltmeter in parallel.

Asked by comparing ammeter and voltmeter connection or resistance, or by asking how a galvanometer is converted to each.

No directly related past PYQ was found.

• practice — not a real PYQ

  To convert a galvanometer into an ammeter, we connect

  • (a)a high resistance in series
  • (b)a low resistance (shunt) in parallel
  • (c)a high resistance in parallel
  • (d)a low resistance in series

  Answer(b) a low resistance (shunt) in parallel — this lets most current bypass the coil, giving a low-resistance ammeter.

• practice — not a real PYQ

  An ideal voltmeter should have

  • (a)zero resistance
  • (b)low resistance
  • (c)infinite resistance
  • (d)a resistance equal to the circuit

  Answer(c) infinite resistance — so it draws no current and does not disturb the voltage it measures.